The conventional power saws are generally provided with a movable protective cover, which is operated by a device consisting of a connection rod provided with a slide slot, and of an eccentric wheel or cam.
Such a prior art device as described above is generally defective in design in that it is exposed and unprotected, and that it undermines the aesthetic effect of the power saw, and further that it is vulnerable to damage caused by the external force, and still further that the moving locus curves of the moving parts of the device is susceptible to distortion caused by the mechanical wear of the moving parts of the device.